This invention relates to novel radiopaque acrylic particles useful in the manufacture of biomedical devices. More particularly, it relates to the incorporation of radiopaque pigments in acrylic resins formed into beads through suspension polymerization which results in a uniform dispersion imparting a precise color control and radiopaque quality to acrylic particles useful for biomedical applications.
Radiopaque particles incorporated in biomedical devices and dental applications allow location of the device by X-ray examination. In particular, the removal and total retrieval of any injected, imbedded, or aspirated acrylic material after insertion arising from broken, damaged or displaced parts is facilitated by the use of radiopaque acrylic resin in the manufacture of the device. The site of such foreign bodies containing radiopaque particles can be quickly and conveniently located by X-ray examination.
In dental applications, a further advantage lies in the fact that the use of radiopaque material also allows for proper placement of dental bridges, and detection of voids and secondary caries. Also, improper contour and over-hangs can be detected and corrected, thereby eliminating broken, damaged or displaced parts.
Typically, in the prior art the radiopaque material has been incorporated into the biomedical device by use of colored heavy metal X-ray opaque compounds which are ball milled with the polymer beads or granules (U.S. Pat. No. 3,715,331) resulting in externally attached radiopaque pigment.
Also metal fillers, such as lead foil, silver alloy, gold and 1% powdered set amalgam have been used to render acrylic based biomedical material radiopaque. However, incorporation of such metal fillers causes stress concentrations at the interface between the insert and the resin which may weaken and fracture the material. Also, addition of the set amalgam produces a grey colored base which is esthetically undesirable.
Barium salts, such as barium sulfate, barium fluoride, barium polyacrylate and copolymers of barium acrylate and methyl methacrylate have also been used to supply radiopaque material. It has been found that increasing the barium sulfate level in the resin to 20% is necessary to render the resin sufficiently radiopaque. However, at this elevated level there is a negative impact on the strength of the acrylic material.